It is best to go back to the HSA interview (Federal->Deductions & Credits->Medical->HSA, MSA Contributions) and change the answers.
However, sometimes, because of the dynamic nature of the flow of the data entry screens, you may find it difficult to get back to the exact screen that you need to change; in this case, I suggest you delete all your HSA information and start over.
1. make a copy of your W-2(s) (if you don't have the paper copies)
2. delete your W-2(s) (use the garbage can icon next to the W-2(s) on the Income screen
3. go to View (at the top), choose Forms, and select the desired form. Note the Delete Form button at the bottom of the screen.
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3. go to Tax Tools (on the left), and navigate to Tools->Delete a form
4. delete form(s) 1099-SA (if one), 8889-T, and 8889-S (if one)
5. go back and re-add your W-2(s), preferably adding them manually
6. go back and redo the entire HSA interview.
Continue with your return.